1. Field of the Invention
This invention relates in general to improved means and method for providing metallization areas on electronic devices, and, more particularly, to improved means and method for providing bonding, resistor, and contact areas on semiconductor devices which must withstand high operating temperatures.
2. Background Art
Electronic devices, particularly semiconductor devices are sensitive to heat. If the devices are exposed to excessive temperatures during manufacturing or use, degradation occurs and the devices fail after a relatively short period of operation. It is generally accepted that most device failure modes are exponentially accelerated as temperature increases. For this reason, many present day semiconductor devices are limited to maximum junction operating temperatures below 100.degree. C. While some devices are able to operate at higher temperatures, e.g., 100.degree. to 150.degree. C., and a few rare devices up to 200.degree. C., these in general do not include a broad range of semiconductor materials or device functions.
With ultra-high speed or ultra-high frequency devices it is often necessary to operate the devices at high current densities. Junction temperature increases as current density increases. As a consequence, very fast devices must be able to tolerate junction temperatures exceeding 150.degree.-200.degree. C. for significant periods of time without excessive degradation. Prior art structures and fabrication methods which provide satisfactory operating life for devices intended for operation in the range below 100.degree. C. or even up to 150.degree. C., no longer are useful for devices which must operate for significant periods above 150.degree. C., particularly above 200.degree. C. For example, contact alloying, emitter punch-through, bond or bonding pad lifting, and resistor degradation occur at an accelerated rate at these temperatures and can unduly shorten device life.
Many high speed devices contain resistors for ballasting or other purposes. It is generally desired that these resistors remain relatively constant with temperature. This restricts the choice of useful resistor materials and can lead to conflicting process requirements, especially as one attempts to deal with other problems such as emitter punch-through from contact alloying. A further complication is the need to have especially robust leads and bonding pads which exhibit high tensile strength, that is, be especially resistant to bond lifting or bonding pad lifting, so that high speed automated assembly equipment may be used. In general the tensile force exerted during bonding increases as the bonding speed is increased.
Thus, there is a need for improved means and methods for electronic devices, particularly, semiconductor devices which must operate at high temperatures and where conflicting requirements exist with respect to bond strength, process economy, contact alloying and punch-through, and temperature stable resistors, and where these conflicting requirements must be simultaneously satisfied.
Accordingly, it is an object of the present invention to provide an improved means and method for obtaining high strength bonds to electronic devices.
It is a further object of the present invention to provide an improved means and method for obtaining metal semiconductor contacts which are substantially free of alloying punch-through.
It is an additional object of the present invention to provide an improved means and method for obtaining integrated resistors on device structures.
It is a further object of the present invention to provide an improved means and method for avoiding bonding pad lifting in devices employing resistor films, particularly where such resistor films underlie the bonding pads.
It is a still further object of the present invention to provide an improved means and method for achieving the above objectives simultaneously.